// 宽度高度 默认100%
@mixin w-h($width:100%,$height:100%){
  width: $width;
  height: $height;
}
//弹性布局
@mixin d-flex ($jc: center, $ai: center, $direction: row,$wrap: wrap){
  display: flex;
  justify-content: $jc;
  align-items: $ai;
  flex-direction: $direction;
  flex-wrap: $wrap;
}